Avidity Biosciences Announces the Accelerated Approval Regulatory Pathway in the US is Open for Del-Brax & Initiates the Global, Confirmatory Phase 3 FORWARD Study in FSHD

Avidity Biosciences, Inc. recently announced the accelerated approval regulatory pathway in the United States is open for delpacibart braxlosiran (del-brax) in the treatment of facioscapulohumeral muscular dystrophy (FSHD). Additionally, the Company announced that it has initiated its global, confirmatory, Phase 3 FORWARD study intended to support a subsequent full approval package for del-brax for people living with FSHD in the US and additional countries around the world.

Del-brax is the first investigational therapy designed to treat the underlying cause of FSHD by directly targeting the disease-causing gene, double homeobox 4 (DUX4). Currently, there are no approved therapies for the treatment of FSHD, a rare, hereditary disorder marked by life-long, relentless loss of muscle strength and function, significant pain, fatigue, and progressive disability. FSHD affects approximately 45,000 to 87,000 people in the US and Europe.

“Our regulatory and clinical development progress announced today reflect our continued leadership in rare neuromuscular diseases and bring us a step closer to providing a treatment option to the FSHD community that could meaningfully impact their disease,” said Sarah Boyce, President and Chief Executive Officer at Avidity. “We have confirmed with the FDA that the accelerated approval pathway is open for del-brax. In addition, we have initiated our global confirmatory Phase 3 study intended to support our global approval strategy for del-brax.”

In addition to the standard guidance for the accelerated approval pathway, the company has been given detailed direction by FDA on the necessary validation steps for the surrogate biomarker. FDA’s Accelerated Approval Program was instituted to allow for earlier approval of drugs that treat serious conditions, and fill an unmet medical need based on a surrogate endpoint.  A surrogate endpoint is a marker, such as a laboratory measurement, radiographic image, physical sign or other measure that is thought to predict clinical benefit but is not itself a measure of clinical benefit. The use of a surrogate endpoint can considerably shorten the time required prior to receiving FDA approval. Drug companies are still required to conduct studies to confirm the anticipated clinical benefit.

To support full approval Avidity has initiated FORWARD, a global, confirmatory, Phase 3, randomized, placebo-controlled, double-blind, 18-month study designed to evaluate 2mg/kg of del-brax every six weeks in approximately 200 people (ages 16-70) living with FSHD in North America, Europe and Japan. FORWARD is designed to assess key FSHD-related endpoints that measure functional mobility (10MWRT and TUG), strength (QMT) and patient-reported outcomes. The flexible design of FORWARD allows the Company to gather additional data from the ongoing FORTITUDE biomarker cohort and elevate any of these measures to the primary endpoint. Currently, QMT is assigned as the primary endpoint.

“People living with FSHD experience severe and unpredictable muscle loss, along with the constant uncertainty of how the disease will progress,” said Mark Stone, CEO of FSHD Society. “We are grateful to Avidity for their innovative approach that takes into account feedback from our community, specifically in the development of a biomarker that provides insights into the real, whole-body burden of FSHD. This research enables the pursuit of a regulatory pathway that may make del-brax available to the FSHD community more quickly. This progress, along with the initiation of the FORWARD Phase 3 study and the stellar del-brax data from FORTITUDE, offers real hope for those urgently needing treatment options.”

FORWARD is a global, confirmatory Phase 3, randomized, placebo-controlled, double-blind, 18-month study designed to evaluate delpacibart braxlosiran (del-brax) in approximately 200 people (ages 16-70) living with FSHD. The trial will be conducted at approximately 45 global sites including in the US, Canada, Europe, and Japan. Patients will be administered either 2 mg/kg of del-brax or placebo (1:1) every six weeks. Following regulatory alignment, FORWARD is designed to be a confirmatory study to support potential full approval of del-brax. FORWARD is assessing the impact of del-brax on key FSHD-related endpoints that measure functional mobility (10-Meter Walk-Run test, or 10 MWRT, and Timed Up and Go, or TUG), strength (quantitative muscle testing, or QMT, total score), patient-reported outcomes (PROs) and decrease in KHDC1L, a novel, circulating biomarker. All study participants, regardless of whether they receive active treatment or placebo, will have the option to enroll into an open-label extension trial. For more information about the FORWARD trial, visit the FORWARD study website.

The FORTITUDE trial is a randomized, placebo-controlled, double-blind, Phase 1/2 clinical trial designed to evaluate single and multiple doses of delpacibart braxlosiran or del-brax in 90 participants with facioscapulohumeral muscular dystrophy (FSHD). FORTITUDE is evaluating the safety, tolerability, pharmacokinetics, and pharmacodynamics of del-brax administered intravenously. Activity of del-brax is being assessed using key biomarkers, including DUX4-regulated muscle and circulating biomarkers and magnetic resonance imaging (MRI) measures of muscle volume and composition. Though the Phase 1/2 trial is not statistically powered to assess functional benefit, it explores the clinical activity of del-brax including measures of functional mobility and muscle strength as well as patient reported outcomes and quality of life measures.

The trial has a total of three dose cohorts. The first two dose escalation cohorts evaluated 2 mg/kg or 4 mg/kg of del-brax versus placebo and were designed to assess safety as well as inform the dose and dose regimen of del-brax for additional studies. Avidity has completed enrollment in the dose escalation cohorts and identified 2 mg/kg every six weeks of del-brax as the dose for future clinical trials.

The third, ongoing biomarker cohort in the FORTITUDE trial assesses the impact of del-brax 2 mg/kg every six weeks versus placebo for 12 months in people living with FSHD, ages 16-70. The primary endpoint of the biomarker cohort is reduction of KHDC1L, a novel DUX4-regulated circulating biomarker. Enrollment in the biomarker cohort is complete and blinded treatment is ongoing.

Participants who complete FORTITUDE have the option to enroll in the ongoing FORTITUDE open-label extension (FORTITUDE-OLE™) study evaluating the long-term safety and tolerability of del-brax in participants living with FSHD. For more information about the FORTITUDE trial, visit the FORTITUDE study website or visit http://www.clinicaltrials.gov and search for NCT05747924. For more information on the FORTITUDE-OLE study click here or visit http://www.clinicaltrials.gov and search for NCT06547216.

Del-brax is designed to treat the underlying cause of FSHD, which is caused by the abnormal expression of a gene called double homeobox 4 or DUX4. The abnormal expression of DUX4 protein leads to changes in gene expression in muscle cells that are associated with the life-long, progressive loss of muscle function in patients with FSHD. Del-brax aims to reduce the expression of DUX4 mRNA and DUX4 protein in muscles in people with FSHD. Del-brax consists of a proprietary monoclonal antibody that binds to the transferrin receptor 1 (TfR1) conjugated with a siRNA targeting DUX4 mRNA. Del-brax is currently in registrational-stage studies including FORTITUDE biomarker cohort and the global, confirmatory, Phase 3 FORWARD trial in individuals with FSHD. The U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) have granted Orphan designation for del-brax and the FDA has granted del-brax Fast Track designation.

Facioscapulohumeral muscular dystrophy (FSHD) is a rare, progressive, and variable hereditary muscle-weakening condition marked by life-long, relentless loss of muscle function, significant pain, fatigue, and progressive disability. It is characterized by progressive and often asymmetric skeletal muscle loss that initially causes weakness in muscles in the face, shoulders, arms and trunk and progresses to weakness in muscles in the lower body. FSHD is an autosomal dominant disease caused by the aberrant expression of the DUX4 (double homeobox 4) gene in the skeletal muscle, which activates genes that are toxic to muscle cells and leads to a series of downstream events that result in skeletal muscle wasting and compromised muscle function. Skeletal muscle weakness results in physical limitations throughout the whole body, including an inability to lift arms for more than a few seconds, loss of ability to show facial expressions and serious speech impediments. These symptoms cause many people affected by FSHD to become dependent on the use of a wheelchair for mobility. Currently, there are no approved treatments for people living with FSHD.

Avidity Biosciences, Inc.’s mission is to profoundly improve people’s lives by delivering a new class of RNA therapeutics – Antibody Oligonucleotide Conjugates (AOCs). Avidity is revolutionizing the field of RNA with its proprietary AOCs, which are designed to combine the specificity of monoclonal antibodies with the precision of oligonucleotide therapies to address targets and diseases previously unreachable with existing RNA therapies. Utilizing its proprietary AOC platform, Avidity demonstrated the first-ever successful targeted delivery of RNA into muscle and is leading the field with clinical development programs for three rare neuromuscular diseases: myotonic dystrophy type 1 (DM1), Duchenne muscular dystrophy (DMD) and facioscapulohumeral muscular dystrophy (FSHD). Avidity is also advancing two wholly-owned precision cardiology development candidates addressing rare genetic cardiomyopathies. In addition, Avidity is broadening the reach of AOCs with its advancing and expanding pipeline including programs in cardiology and immunology through key partnerships. Avidity is headquartered in San Diego, CA. For more information about our AOC platform, clinical development pipeline and people, please visit www.aviditybiosciences.com and engage with us on LinkedIn and X.